740 VERHOEFF AND BELL. 



vision, persistent and annoying after images and fatigue due to efforts 

 to overcome the difficulties of vision under these disadvantages. As 

 regards definite pathological effects or permanent impairment of 

 vision from exposure to the luminous rays alone we have been unable 

 to find either clinically or experimentally anything of a positive nature. 

 The experiments on monkeys, which we have recorded, show very 

 clearly that exposure to light of intensity many times greater than 

 anything to be found in the use of commercial illuminants produced 

 only temporary scotomata. The lid reflexes appeared within a very 

 few minutes and the scotomata seemed to have worn away within at 

 most a few hours. There was not the slightest sign of permanent 

 impairment of vision. As noted on page 684 there were indications 

 that the process of light adaptation may go on to a considerable degree 

 even during very severe exposure to light. In the experiments on the 

 human eye results were found closely comparable with those obtained 

 in the earlier experiments on monkeys. The erythropsia passed away 

 in a few minutes and the scotoma wore away rapidly so that after 

 three hours the visual acuity was normal, although there still remained 

 traces of color scotoma. After 22 hours visual acuity remained normal 

 and the central color vision for red, blue and green was also normal. 

 This intensity of the light in this case was far in excess of anything 

 which could be reached in the use of commercial illuminants and 

 there was a length of fixation many times greater than could ever 

 be found in practical use of lights. These experiments seemed con- 

 clusive in showing that the effect of even extraordinarily severe 

 exposure to luminous rays produces only such temporary effects as 

 might reasonably be expected and is followed by no lasting injuries 

 of any kind. Whether frequent and long exposures of a similar kind 

 might exhaust the extraordinary recuperative powers of the eye is a 

 matter on which in the nature of things there can be no direct ex- 

 perimental evidence and which is not of practical importance since 

 under no working conditions could even a single exposure compar- 

 able in severity with those obtained in our experiments be produced. 

 There is, however, very strong clinical evidence that even severe daily 

 exposures to intense light lasting over many years fails to produce 

 material injury to the eye. For in the case of glass blowers there is 

 extreme exposure both to the heat and light of the furnace occurring 

 daily for many years. While glass blowers' cataract, probably arising 

 as we have shown from secondary causes quite aside from the direct 

 effects of radiation, may be produced under these circumstances, 

 there has never been noted any injury to the retina. The fact that 



